A number of various lathe system to process components/workpieces are known from the state of the art. The meshing of the cutting edge of a tool with a rotating workpiece results in a chip which is lifted of the workpiece surface. Besides processing metal workpieces, processing of plastic parts with a lathe system has become significantly important, especially when manufacturing optical lenses.
The market share of plastic optical lenses made from blanks has increased drastically. In order to optimize different properties of plastic optical lenses, new plastics have been developed in the recent years for optical applications. Especially impact resistant materials are important in this respect. High impact resistance offers good eye protection, illustratively for motor bikers against flying stones or for persons that are exposed to dangerous flying particles for example while working on a workbench.
Particular polycarbonate spectacle lenses have been used for this purpose. This material has a high degree of density and therefore an extremely good impact resistance. When being processed on a lathe such tenacious materials result in non-breaking and therefore very long flowing chips. This feature is advantageous in particular when processing high accuracy optical plastic parts, because chip breaks do not occur, especially not in the immediate vicinity of the cutting zone, that otherwise might entail unevenness on the processed surface.
Preferentially the processing of the surface is performed in a way that only a single flowing chip is generated in each mashing of the cutting edge of the tool with the plastic part or the respective blank. This is especially desired for the final material removal using a diamond lathe to manufacture an optical lens surface of the highest possible quality. Any chip break would result in damages on the lens surface and could not be remediated by the subsequent polishing stage.
Material removal resulting in a mono-flowing chip has the disadvantage that the motion behavior of the very long flowing chip is unpredictable. The long flowing chip might move into rotating lathe components, for instance into a rotating workpiece receptacle wherein it may be tensile stressed until it is been turned off. These tensile loadings may cause irregular material removal in the cutting zone, resulting in irremediable unevenness on the lens surface being processed.
A long flowing chip with a cross-section of about 0.1 by 0.03 mm, winds itself around the turning workpiece receptacle from which it must be subsequently removed by hand. This is resulting in frequent machines stoppages and increased labor costs. If the long flowing chip is not removed by hand, the automated loading of plastic parts has to be stopped because a chip in the area of a collet chuck of said receptacle causes insertion errors.
The state of the art attempts remedying the above disadvantageous by redirecting the chip away from the cutting edge of the tool. Presently water ejecting nozzles are used for that purpose. These ejecting nozzles use comparably high water pressure to deflect the chip, in order to preclude it from being entangled with the workpiece receptacle or with the tool spindle. Other devices are known that redirect the chip by using a vacuum suction device.
Such devices have the disadvantage that a water jet directed to the chip induces oscillations and vibrations in said chip, which negatively effects the chip removal at the cutting side. In particular polycarbonate is susceptible to chip vibrations. In particular the chip skips in and out of the water jet. Consequently this leads to volatile tension loading on the chip and results in an uneven process surface.
Moreover the parts impacted by the water jet start to vibrate. In particular the tool with its cutting edge and the workpiece will vibrate. This leads to nano-defects on the processed surface. These effects can hardly be eliminated by the subsequent polishing. Additionally, the jet of liquid of known devices has a comparatively small cross-section, which allows a flowing chip to move outside this radius of action of the jet of liquid.
While the variant of a vacuum suction does relatively reliable remove the flowing chip, a problem remains because there is no cooling in the cutting zone during cutting. As a result there are undesired increases in temperature which negatively affects the tools cutting quality and the material properties of the process plastic part. Illustratively the plastic part may bear burning marks or may undergo plastic deformations.
Accordingly it is the objective of the present invention to eliminate the disadvantageous of the state of the art and to provide a method to process a plastic part by a lathe system, as well as a lathe system implementing said method, resulting in processed plastic parts having a high surface quality. Particular problems solved by the present invention are the chip removal and the cutting zone cooling. Also, the solution of the present invention shall be highly reliable easily applicable and economical.